The present invention relates to a vacuum valve controller for controlling a vacuum valve for use in a vacuum transfer system for transferring soil water accumulated in a soil water basin to a predetermined place, such as a sewage disposal plant. The vacuum transfer system sucks the soil water from the soil water basin through a suction pipe by opening the vacuum valve.
There has been proposed a vacuum soil water transfer system which utilizes a vacuum for transferring soil water accumulated in each of a plurality of broadly distributed soil water basins to a predetermined place, such as a sewage disposal plant. In such a vacuum soil water transfer system, each soil water basin is provided with a soil water suction pipe, a vacuum valve for selectively communicating the suction pipe with a vacuum system and a vacuum valve controller for controlling the vacuum valve to open and close depending on the level of the soil water accumulated in the soil water basin.
FIGS. 3 and 4 show an exemplified system arrangement using a prior art vacuum valve controller of the type described above, which is disclosed in Japanese Patent Application No. Hei-7-39362 (No. 39362/1995). In FIGS. 3 and 4, reference numeral 1 denotes a soil water basin, which is provided with a suction pipe 3 having a distal end disposed in the soil water basin 1 and a proximal end connected to a line 5 (forming a part of a vacuum system) through a vacuum valve 4 having a valve body 6. The line 5 is in communication with a vacuum tank (not shown). The vacuum valve 4 further includes a diaphragm 4b and a spring 4a for biasing the diaphragm 4b, both housed in a piston chamber 4c.
Reference numeral 11 denotes a controller, which comprises a casing 12 having a large-diameter portion 12a and a smaller-diameter portion 12b contiguous to the larger-diameter portion 12a. The larger-diameter portion 12a has a partition wall 15 formed therein substantially at the center of the larger-diameter portion 12a and dividing the inside of the larger-diameter portion 12a into left- and right-hand regions. The partition wall 15 has a hole formed therein through which extends a shaft 14 supporting a valve body 13. The left-hand region, in turn, is divided into first and second pressure chambers 17 and 18 by means of a first diaphragm or a sensor diaphragm 16 provided substantially at the center of the left-hand region. The right-hand region, in turn, is divided into third and fourth pressure chambers 20 and 21 by means of a second diaphragm 19 provided substantially at the center of the right-hand region. Further, the inside of the smaller-diameter portion 12b is divided into left- and right-hand regions by means of a partition wall 22. The left-hand region of the smaller-diameter portion 12b defines a chamber which is contiguous to and in communication with the fourth chamber 21. The right-hand region of the smaller-diameter portion 12b, in turn, is divided into fifth and sixth pressure chambers 24 and 25 by means of a partition wall 23.
The valve body 13, which is secured to a distal end of the shaft 14, is disposed in the sixth chamber 25. The proximal end of the shaft 14 is fixedly secured to the first diaphragm 16 at the center thereof by means of a screw 14a. The shaft 14 extends through the partition wall 15, as well as through the second diaphragm 19 (which is fixedly secured to the shaft 14). The shaft 14 further extends through the partition walls 22 and 23. A seal 26 is provided between the shaft 14 and the partition wall 15 and another seal 27 is provided between the shaft 14 and the partition wall 22. The partition wall 23 has a through hole 23a formed therein, through which the shaft 14 extends, and which may be closed by the valve body 13. A spring 28 is provided for urging the second diaphragm 19 in a leftward direction seen in the figure.
A magnet 29 is provided on the rear end wall of the casing 12 at a position where it faces the rear end (or the proximal end) of the shaft 14, and more specifically the above-mentioned screw 14a made of a suitable ferromagnetic material and which is threadingly secured to the rear end of the shaft 14. The sixth chamber 25 has a hole 30 for communicating with the atmosphere, which may be opened or closed by the valve body 13. The suction pipe 3 has pressure detection holes 9 and 10 provided at different levels, with a predetermined spacing in the vertical direction defined between the holes 9 and 10. One pressure detection hole 9 is in communication with the fourth chamber 21 through a pipe 31, while the other pressure detection hole 10 is in communication with the third chamber 20 through a pipe 32. A pressure sensing tube 2 is disposed in the soil water basin 1 and in communication with the first chamber 17 through a pipe 33. The second chamber 18 is in communication with the atmosphere through a hole 34. The fifth chamber 24 is in communication with the line 5 through a pipe 35 and the sixth chamber 25 is in communication with the piston chamber 4c of the vacuum valve 4 through a pipe 36.
In the vacuum valve controller having the above arrangement, as the level of soil water in the soil water basin 1 rises, the pressure in the pressure sensing tube 2 builds up, and this pressure is led through the pipe 33 into the first chamber 17 in the controller 11. By means of the pressure in the first chamber 17, the first diaphragm 16 is displaced in the rightward direction against the biasing force of the spring 28 as well as against the magnetic attraction force of the magnet 29, so that the shaft 14 is displaced in the right direction to cause the valve body 13 to close the hole 30 communicating with the atmosphere. Thus, the vacuum in the line 5 is led through the pipe 35 into the fifth and sixth chambers 24 and 25, and thence into the piston chamber 4c of the vacuum valve 4. By this, the valve body of the vacuum valve 4 is lifted away from the valve seat 7.
In the above sequence of operations, when the first diaphragm 16 is displaced by the pressure built-up in the pressure sensor tube 2 and the shaft 14 starts to move, the biasing force provided by the spring 28 gradually increases with the displacement of the shaft 14, while the attraction force provided by the magnet 29 suddenly decreases (proportional to the square of the displacement). Accordingly, the shaft 14 snaps into its displacement limit, or closing position, where the hole 30 is closed by the valve body 13. It should be noted that the holes 23a and 30, the fifth and sixth chambers 24 and 25, the valve body 13 and the shaft 14 together form a vacuum valve actuating means for opening and closing the vacuum valve 4.
When the valve body 6 is lifted away from the valve seat 7, the line 5 and the suction pipe 3 are communicated with each other, so that soil water in the soil water basin 1 is sucked into the line 5 through the suction pipe 3. This produces a pressure difference between the pressure detection holes 9 and 10, and the different pressures at the pressure detection holes 9 and 10 are led through the pipes 31 and 32 to the fourth and third chambers 21 and 20, respectively. As a result, the pressure difference therebetween acts on the second diaphragm 19 to displace it in a rightward direction, so that the valve body 13 is further pressed against the hole 30 through the shaft 14. Thus, as the level of soil water in the soil water basin 1 is lowered by sucking the soil water from the basin 1, and even the pressure difference between the first and second chambers 17 and 18 is reduced to zero, the valve body 13 remains pressed against the hole 30 by virtue of the rightward force provided by the pressure difference between the fourth and third chambers 21 and 20. The pressure difference lasts as long as soil water flows into the line 5 through the suction pipe 3.
When the soil water level in the basin 1 is further lowered and air begins to be sucked into the suction pipe 3 through its lower end, the pressure difference between the pressure detection holes 9 and 10 is lost. Consequently, the second diaphragm 19 is displaced in the leftward direction by means of the spring 28, so that the valve body 13 is pressed against the through hole 23a formed in the partition wall 23 to close the through hole 23a. Since the hole 30 is thus opened, atmospheric air flows into the sixth chamber 25 through the hole 30, and thence into the piston chamber 4c of the vacuum valve 4 through the pipe 36. As the result, the valve body 6 is moved back into the closed position by the biasing force of the spring 4a. Thus, the valve body 6 closes the valve port in the valve seat 7 and shuts off communication between the suction pipe 3 and the line 5.
The prior art vacuum valve controller having the arrangement described above, however, suffers from a problem as follows. Namely, in a case where a leakage occurs in the pressure sending tube 2 and when a water level in the basin 1 is lowered, a soil water column may be formed in the pressure sensing tube 2. In another case, it is also possible that the vacuum valve controller 11 and the pressure sensing tube 2 are initially connected to each other with a soil water column inadvertently left in the pressure sensing tube 2. In either case, the pressure in the pressure sensing tube 2 becomes negative when the soil water in the basin 1 is sucked through the vacuum valve 4, thereby lowering the soil water level in the basin 1 to a certain level near the lower end of the suction pipe 3. Due to the negative pressure in the pressure sensing tube 2, the first diaphragm 16 may be displaced back to its standby position or leftward limit position forcibly. If this occurs, the shaft 14 is also moved back to its standby position, and, thus, the valve body 6 of the vacuum valve 4 forcibly closes the valve port in the valve seat 7 while the soil water is sucked from the basin 1. This results in an occurrence of water-hammer in a region of the vacuum valve 4 upstream of the valve body 6, which leads to a possible, unintended disconnection of the vacuum valve 4 from the suction pipe 3.
In view of the foregoing, it is an object of the present invention to provide a vacuum valve controller for controlling a vacuum valve, which can prevent any forced closing of the vacuum valve during suction of soil water from a soil water basin, even when a soil water column is formed in a pressure sensing tube due to a possible leakage occurring in the sensing tube or for some other reason, and which ensures that the vacuum valve is actuated to close only after air is sucked through the suction pipe.